1. Field of the Invention
The present invention relates to an image forming apparatus such as a copy machine or laser printer having a secondary or auxiliary cassette feeder for enhanced paper loading capacity and, more particularly, to a secondary cassette feeder for introducing sheets of paper to the main system using the same driving force as the primary feeder.
2. Description of the Related Art
To general, image forming apparatus produce images on sheets of print media (e.g. paper) which are feed into the machine one sheet at a time using a cassette feeder. A separate feeder is often used to increase the paper capacity or enhance the operation.
In the operation of earlier laser printer, a print signal is supplied from a computer or, in the case of a copy machine, from a microprocessor. The print signal activates a first pick-up roller which draws a sheet of paper loaded on a first knock-up plate. The selected sheet of paper is then guided around a guide roller through a pair of friction rollers and, using a drive motor, is conveyed to a transferring roller charged to a high voltage.
Meanwhile, a scanning unit generates a laser beam corresponding to video signals input from the computer and scans a drum to form an electrostatic latent image thereon which is developed using toner in a developer. The leading edge of the traveling sheet of paper meets with the developed images on trip drum at a specific point according to a synchronizing signal, whereupon the toner image is transferred onto the paper. The final image is formed by a fixing unit which fuses the toner to the paper using high temperature.
A secondary cassette feeder is provided below a main body, for feeding auxiliary sheets of paper loaded on a second knock-up plate. An electrical connector is required to supply the computer's synchronizing signal and a power supply voltage front the main body to the lower portion of the system. A second pickup roller is driven by a separate motor, through a series of timing gears, to convey the paper up through a second pair of friction rollers to the friction rollers of the main body. Thereafter, the above-described print processes are performed via the driving force from the motor of the main body.
Accordingly, the earlier second cassette feeder is driven separately, which inherently leads to synchronization problems. As a result, paper jamming and shredding may occur, which wastes paper and is an inconvenience to the user. Also, if the separate motors are even slightly out in sync as they are driven, the system tends to be noisy such that the mechanism undergoes undue wear and tear. In addition, the separate motors require more gearing and associated components and wiring in order to transfer the driving force to the lower portion of the secondary cassette feeder, thereby increasing the cost of manufacture as well as the size of the system.